1. Field of the Invention
The present invention relates to a pipe joint made of resin, in particular, such a pipe joint applied to laying pipes for a high-purity liquid, ultra pure water and a medical liquid or the like used in a production process such as the production of semiconductor, medical supplies and medicines, food processing, and chemical industry.
2. Description of the Prior Art
Conventionally, such a pipe joint made of resin having a structure like that shown in FIG. 8 is known. The pipe joint made of resin shown in the same figure comprises a joint body 81, an inner ring 82 and a pushing ring 83. The joint body 81 has a receiving port 84, a tapered receiving surface 85 projecting from a base portion of the receiving port 84, and a tapered receiving surface 86 disposed on a tip portion of the receiving port 84. Additionally, an outer periphery of the receiving port 84 is provided with a male thread portion 87. The inner ring 82 includes a connecting portion 89 having a swelling or bulge portion 88 whose section is mountain-like or chevron-shaped, and a projector protruding portion 90. A tip of the protruding portion 90 is provided with a tapered primary seal urging face or abutting surface 91. The pushing ring 83 includes a pressing portion 92.
According to the known pipe joint made of resin, a diameter of an end portion of a pipe 7 made of resin forcedly inserted in the connecting portion 89 is increased, thereby forming a tapered abutting surface 93 on an outer surface of the pipe 7. The end portion of the pipe 7 is inserted into the connecting portion 89, the inner ring 82 connected to the pipe 7 is forcedly inserted in the receiving port 84 of the joint body 81 with the result that a female thread portion 94 of the pushing ring 83 previously fitted in the pipe 7 is threadedly connected to a male thread portion 87 of the receiving port 84, thus being fastened. Then, the pressing portion 92 of the pushing ring 83 pushes the inner ring 82 in a pressing direction, and the abutting surface 91 of the inner ring 82 forcedly abuts against the receiving surface 85 of the joint body 81, thereby forming an axial sealing portion SA, and the abutting surface 93 of the pipe 7 forcedly abuts against the receiving surface 86 of the receiving port 84, thereby forming an axial sealing portion SB.
In the conventional pipe joint made of resin shown in FIG. 8, the pushing ring 83 is fastened, thus generating a pressing-directional pressing force. Consequently, the sealing portions SA and SB are formed on two regions, and a sealing surface pressure in an axial direction is generated on the sealing portions SA and SB. Therefore, a creep and a stress relaxation with the passage of time are generated on the joint body 81 made of resin and the pushing ring 83, the pipe 7 or the like, whereby the sealing surface pressures of the sealing portions SA and SB are decreased with the result that there has been concern that the sealing property is lost relatively early.
Furthermore, in order to secure a predetermined sealing property, an amount of thread connecting the pushing ring 83, a fastening torque or the like are controlled in high accuracy, a fastening force generated by the pressing ring 83 has been required to be strictly set at a predetermined magnitude. Therefore, there are problems wherein an operating efficiency is lowered and high technique and skill are required in operation.